From daf4c9fadaf8a49198c53c039bf78980dc251a4b Mon Sep 17 00:00:00 2001
From: Hans de Goede <hdegoede@redhat.com>
Date: Tue, 30 Jul 2013 15:57:16 +0200
Subject: [PATCH 1/2] linux: Use a separate lock to serialize start/stop vs
hotplug events
Using one lock for this is a bad idea, as we should not be holding any
locks used by the hotplug thread when trying to stop otherwise the stop
function may wait indefinetely in pthread_join, while the event-thread
is waiting for the lock the caller of the stop function holds.
Using 2 separate locks for this should fix this deadlock, which has been
reported here: https://bugzilla.redhat.com/show_bug.cgi?id=985484
Many thanks to Chris Dickens for figuring out the cause of this deadlock!
CC: Chris Dickens <christopher.a.dickens@gmail.com>
Signed-off-by: Hans de Goede <hdegoede@redhat.com>
---
libusb/os/linux_usbfs.c | 24 +++++++++++++++++-------
libusb/version_nano.h | 2 +-
2 files changed, 18 insertions(+), 8 deletions(-)
diff --git a/libusb/os/linux_usbfs.c b/libusb/os/linux_usbfs.c
index 09288af..90e23b7 100644
--- a/libusb/os/linux_usbfs.c
+++ b/libusb/os/linux_usbfs.c
@@ -120,7 +120,9 @@ static int sysfs_has_descriptors = -1;
/* how many times have we initted (and not exited) ? */
static volatile int init_count = 0;
-/* Serialize hotplug start/stop, scan-devices, event-thread, and poll */
+/* Serialize hotplug start/stop */
+usbi_mutex_static_t linux_hotplug_startstop_lock = USBI_MUTEX_INITIALIZER;
+/* Serialize scan-devices, event-thread, and poll */
usbi_mutex_static_t linux_hotplug_lock = USBI_MUTEX_INITIALIZER;
static int linux_start_event_monitor(void);
@@ -419,7 +421,7 @@ static int op_init(struct libusb_context *ctx)
if (sysfs_has_descriptors)
usbi_dbg("sysfs has complete descriptors");
- usbi_mutex_static_lock(&linux_hotplug_lock);
+ usbi_mutex_static_lock(&linux_hotplug_startstop_lock);
r = LIBUSB_SUCCESS;
if (init_count == 0) {
/* start up hotplug event handler */
@@ -433,20 +435,20 @@ static int op_init(struct libusb_context *ctx)
linux_stop_event_monitor();
} else
usbi_err(ctx, "error starting hotplug event monitor");
- usbi_mutex_static_unlock(&linux_hotplug_lock);
+ usbi_mutex_static_unlock(&linux_hotplug_startstop_lock);
return r;
}
static void op_exit(void)
{
- usbi_mutex_static_lock(&linux_hotplug_lock);
+ usbi_mutex_static_lock(&linux_hotplug_startstop_lock);
assert(init_count != 0);
if (!--init_count) {
/* tear down event handler */
(void)linux_stop_event_monitor();
}
- usbi_mutex_static_unlock(&linux_hotplug_lock);
+ usbi_mutex_static_unlock(&linux_hotplug_startstop_lock);
}
static int linux_start_event_monitor(void)
@@ -469,11 +471,19 @@ static int linux_stop_event_monitor(void)
static int linux_scan_devices(struct libusb_context *ctx)
{
+ int ret;
+
+ usbi_mutex_static_lock(&linux_hotplug_lock);
+
#if defined(USE_UDEV)
- return linux_udev_scan_devices(ctx);
+ ret = linux_udev_scan_devices(ctx);
#else
- return linux_default_scan_devices(ctx);
+ ret = linux_default_scan_devices(ctx);
#endif
+
+ usbi_mutex_static_unlock(&linux_hotplug_lock);
+
+ return ret;
}
static void op_hotplug_poll(void)
diff --git a/libusb/version_nano.h b/libusb/version_nano.h
index ebf41e1..34e26ff 100644
--- a/libusb/version_nano.h
+++ b/libusb/version_nano.h
@@ -1 +1 @@
-#define LIBUSB_NANO 10774
+#define LIBUSB_NANO 10777
--
1.8.3.1